Flirting or Floundering

So I was picking up a prescription the other day and this guy struck up a conversation with me swearing that he knew me from somewhere. I didn't really recognize him, though I still had a feeling I might know this man. Similar in age, weight, height, and style as myself; this almost felt like flirting. I say this because the banter went on for several minutes, both floundering to place where we may have met. Atop of being socially awkward, I've always been terrible at knowing when somebody is flirting with me. The conversation would be how to tell the difference between small talk amongst strangers vs. flirting...