The suit was altered superbly by the tailor, making the timid old man feel like a bold young lion.
I don't understand why the sentence is correct because the word "making" isn't placed after a form of 'be'. But I think it's not a gerund, and I think the word "was" in the beginning of the sentence is for the "altered superbly by the tailor". Please help me to understand the grammar involved here.