I figured it was just for the lulz but your post made me want to look into it. I'm still leaning towards "for the lulz" but... the place actually exists... and people ARE stupid... but is it possible that someone could be THIS stupid?!
Upvote for the research efforts & may be true.
However, seems the address you've found is Linden Blvd, but the original poster is Linden Ave. I'm sure if this was a lost keys poster by someone who lives there would know that.
Secondly, says in the poster "front and back house keys" but its an apartment block (posting says #1a), not a house (ok they might casually refer their own apartment as a house at a push), plus there's also no visible back door on street view. May be hidden but why would someone list exactly what each key fits & not describe what they look like instead?
Some people might make some of the listed mistakes, but not all.
This is either a prank on someone who they want to get burgled or just for laughs. Otherwise its a perfect list of exactly what not to do when you loose your keys.
Police trap houses (yes they exist): Are we a joke to you. A trap house is when the police make a building look like a great target but it has cameras and UV ink on everything so they can catch crooks.
Wouldn't the person being "trapped" need to have found the keys, therefore the police would need to place the keys to be found nearby if this was the case?
The burglars could just turn up & break into apartment #1a before 5pm of course but turning up to break into a car wouldn't be much good without knowing which car it was or having the the key fob to open it but I guess they could just randomly break into a vehicle anyway without keys.