They both write nostalgic rock and roll. Sure there are probably some Japandroids hipster fans who think they are too good for Gaslight, and plenty of Gaslight fans that dismiss Japandroids as hipster bullshit without actually listening to Celebration Rock. And of course, there are the people who legitimately don't like one band or the other. But they are lyrically similar enough and both have good music that I think there is a larger fanbase overlap than you're giving them credit for.
Definitely agree. It's just funny based on the similarities that people think its so different