One clap is a pity clap. I usually come across one clap writers while reciprocating.

I have a scale of claps. If I read something with retched grammar and form, but the writer seems sincere and kind, I'll leave one clap and highlight something. I generally won't try to offer helpful edits or advice because it's too much to even start. Most of the time, I stop reading, but keep the page open for the time Medium estimates a full read if the writer is a member.

Hopefully, they will keep writing and improve.