Exactly, they’re coworkers where OP isn’t certain if they were flirting or just being friendly, and other coworkers confirm she’s flirting. To me that means:

• they don’t have a good enough relationship to tell the difference, so probably not "friends"
• other coworkers don’t seem to experience the same thing
• claims to not have other friends (surely she’d mention a BF, no?)

So to me, that sounds very much like she’s flirting, so it’s totally understandable for OP to consider it a date.