Is my teacher just being friendly or is this flirting?

My teacher (M30something) asked me (F18) to go play tennis with him after school and after a few days he asked again.
He is always very nice to students, but is this also considered being friendly or could it be considered flirting? I mean, it's not very common for a male teacher to ask a younger, female student to do something together just the two of them outside of school, is it?
But I don't know, maybe I'm reading too much into it and he just wanted to go play tennis with someone lol.

PS He asked because he found out I play tennis, and he also enjoys this sport.
Is my teacher just being friendly or is this flirting?
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