And this has little correlation with the space guy incident.
He's just trying to find some "SOLID EVIDENCE IN MY PROSECUTION"
From what I've seen, it's quite obvious why Spock is bringing up the Space Guy argument:
Spock is bringing it up because it's a fairly similar situation, except in this case you are Space Guy and he is you. He asked you to make a Medieval weapons pack; you didn't. Later on, after getting kicked out of his clan, you decide it's a good idea and begin working on it. (Not exactly the same as the Riot Shield situation but relatively the same)
I don't know, it seems that you are doing this because:
A) You feel like it and think it's a good idea
B) You want to make Spock jealous (probably from Spock's perspective)
More reasonably, I would say A but, once again, I cannot be sure.
Spock takes this as competition, basically. You knew what their clan was doing, but you didn't help them out. After getting kicked, now you are making what they are making and it's competition.