I'm not really sure, but if you don't have a large tank one will eventually dominate and chase the other one ALL DAY and I don't think it was foreplay
I had one sharknose and one neon in a 90 gallon tank and the sharknose chased the neon whenever he could see it. Eventually the neon ended up in the sump and I fished him out and put him in my nano tank. I wouldn't recommend 2 neons in anything less than a 75. If you've seen samw's video of his neons fighting its really rather gory how aggressive they can get towards each other.