The hand radical (left-side form of 手) marks 撩 as a deliberate manual action - lifting curtains, flicking water, or in the modern slang sense, reaching out to provoke someone's feelings. Pairs naturally with 拨, 挑 in flirt-and-tease territory.
Lends its sound, with the tone shifting from liào to liáo. It heads a phonetic series with 僚, 寮, 疗 and 燎. The flame meaning is incidental, but it gives a nice mnemonic for the kindle-feelings sense of flirting.