There's plenty of "toys" that adults can enjoy as hobbies. Obviously hobby shops cater to that crowd. I kinda doubt if he was buying model trains or.. funko pops.. anyone would be confused that he was shopping for himself. So I'll echo what ScallionPancake asked: What the fuck is he buying?
A lot of toys may be designed with limitations - an electronic toy music instrument may only play preselected music for example
However some general purpose "toys", like an actual musical instrument, might be "played" with by a child and adult alike
Some "toys" like this are too difficult for unskilled kids to "play" - for example maybe complicated musical instruments or maintaining them
Thus the mismatch is when an adult is looking for limited toys rather than general purpose or adult "toys"... it's like, you can play with "real toys" now, why would you want "kid toys"?
(Maybe another example is a toy car versus an actual car you can drive places with - or playing a video game of driving instead of actually just driving around places)