I [24/F] found women's jeans in my boyfriend's [27/M] load of laundry. We live alone. Am I wrong to be suspicious?

This happened this morning when I was folding a load of laundry that my boyfriend had done last night. The load was mostly his dark-colored clothing, but also had a few towels, etc. thrown in. I noticed a bright mint green item that stuck out from the rest of the laundry, and when I pulled it out it was a pair of women's jeans. They are a size or two larger than anything I've ever worn, and I don't recognize them at all as being anything old I or my boyfriend just had hanging around.
For context, we moved in together about a year ago. We live alone, and haven't even had overnight guests in the time we've lived in this apartment. We have our own washer and dryer in unit, which we bought new from a store when we moved in.
If it was a shared machine, I wouldn't be all that worried, because I know laundry does tend to get mixed together, but I can't help but be concerned. I texted my boyfriend a picture of the jeans, asking if he knows what they are, and he replied no and asked if I was sure they weren't something of mine. When I said I was, he reiterated that he has no idea, and that they must be something we picked up in the move or while traveling and they somehow got into the laundry.
I suppose that's a plausible explanation, but I'm not sure how it happened. I had traveled some this summer, but washed and put away all my clothes months ago and didn't notice any weird items while unpacking. He hasn't traveled to pick up clothes by mistake since last Christmas, and all of the clothing in that load was his. Everything in the laundry besides the pants was frequently used/washed items. I have no reason to suspect him of cheating, but this is just so weird. Am I silly for being worried and, if not, how do I talk to him about it without sounding like I'm accusing him of something? Thanks.
EDIT: Since lots of people have mentioned cross dressing, it's probably relevant to mention that the pants, while a bigger size than I wear, are way too small to fit my boyfriend. The jeans would fit a girl who wore about a women's size small/medium, while boyfriend wears a men's XL. They also look like they've been washed/worn quite a bit, so I don't think they'd be a recently purchased item.
EDIT 2: Lots of comments are mentioning that it would be impossible for a cheating partner to leave without pants on. Since I've traveled some recently, my fear would be that he had someone over for a longer time period who had changes of clothes/an overnight bag and forgot to repack those pants. Or a girl came over after work and changed for a night out, leaving the pants behind. Or stained, lost, etc. her pants and left in clothes of my boyfriends. I don't really think anyone would have left naked.
TL;DR: I Boyfriend and I have lived together for about a year. We live alone in our apartment, and bought our own washer and dryer new when we moved in. Today I found a pair of women's jeans that are not mine in a load of laundry he had washed (mostly his clothes, some household linens). He claims to not know where they came from, and suggested maybe we picked them up by mistake in moving or during a trip. He hasn't traveled in months, and all of the other laundry in the load has been frequently used/washed recently, so I'm not sure how a mystery item would have gotten stuck in there. I have no reason to think he would cheat, but I'm still worried. How should I proceed? Thanks.


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