It's flammable because it contains alcohol, like all toners do to some extent. Nail varnish remover also contains alcohol, or something very similar and equally flammable, so therefore you could probably, if you wanted to waste a lot of money, use Clinique toner as nail varnish remover. You could use most toners the same way, though I'm not sure they'd work that well, as nail varnish remover has other ingredients which toner doesn't have and vice versa, hence the different uses.
I'm not trying to sell you Clinique or anything, it's a personal decision what skincare you prefer; I just thought I ought to point out for the OP that Clinique toner is not just expensive nail varnish remover and is fine to use on your face!