RE: It's not a ladybug, it's a flea beetle. [EN] // [ES]

The fact is that many people think that ladybugs are beetles...

Of course ladybugs are beetles (of the family Coccinellidae)!
The word "bug" in "ladybug" might be misleading, but that's often the problem when using common names instead scientific appellations of insects.

I think the exact beetle species in your post is Alagoasa bipunctata var. perennis (family Chrysomelidae - as you correctly wrote: not a ladybug!).