There's no suggestion of that in the quotation. The author is suggesting that Tinder was designed as a straight hookup app inspired by grindr, the gay hookup app. This is not really true in the specific but certainly isn't implying non-straights are "tending against monogamy".

There isn't an offensive imputation contained in being called non-monogamous anyway, unless you in turn have a prejudice against polyamory etc.