I think of it as BSD style, though of course it could be suggested/mandated elsewhere -

  [...]Use a space after keywords (if, while, for, return, switch). No braces are used for control statements with zero or only a single statement unless that statement is more than a single line, in which case they are permitted.[0]

The good thing is that -Wmisleading-indentation [2] (comes along with -Wall) catches this indentation error.

[0] https://man.openbsd.org/style - happens to be same for at least NetBSD.

[1] https://www.gnu.org/prep/standards/html_node/Syntactic-Conve...

[2] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html