That just depends on how they use it.
If they use it as an insult it could be homophobic, because they think being gay is SO BAD that it will offend people
No, they just use it because it's an insult that's commonly used. Also, I should get this out of the way. I AM NOT A HOMOPHOBE AND SUPPORT THE LGBTQ+ COMMUNITY. I'm just saying that as a person who HAS used gay as an insult, I am not homophobic.