Is it me?

So I have been seeing this guy. I left my glasses at his house one night. So I made arrangements to pick them up the next day. He was going to be gone so I asked him if he could put them on the front porch. When I went to pick them up the next day along with my glasses was a womans white tank top. It was not mine! I was like WTF? Earlier in the relationship we had a long talk about comitment and monogamy and he seemed to be not sure of it all....Anyways when I texted him and said "dude, that's not my tank top who's is it?" he claimed that it was just a "shirt he had for a long time and he thought that I might want it." He then accused me of making assumptions and getting upset about nothing. He called me a "Negative Nancy"! Is it just me or does this situation sound odd?