Is this new terms they have just added recently (maybe this month)?
This, I don't know. I haven't extensively checked their ToS in the past. But I guess it has always been there. I've asked the MineBit team about this, too, just to be sure (I'll inform you once they respond to this).
Because I believe I have wagered a lot in original games since I created my account and I earned EXP with that wager on original games.
I'm quite sure I pushed myself to wager on original games when I was closed to level up to my current rank Knight III and it was working or I managed to level up by playing original games.
Anyway, lets say this term is already there since the first day then there must be also a bug which count wager on original games toward EXP
I see. That sure is quite baffling. I've forwarded this concern to the MineBit team. Let's see how they respond to this.
One suggestion, this term should be also added in their EXP information because currently the only information is $1 wager = 1 EXP with no excluded games information.
I agree; I've made a similar suggestion to the MineBit team already (but that's for them to add it to the VIP/Loyalty FAQ Page). Your suggestion to add it directly on that little tool tip would greatly help. Forwarded this suggestion as well.
One more note: seems that they are responding to you faster than responding to players as there is still no email from them telling me about this case, hope they can improve it.
I guess they just love to hear my input and feedback that I relay to them, which is given by the forum users.

TBH, I only talk to the OP (Pat); she's my point of contact on their team and she then contacts directly to their support staff or core team (I can't confirm it but I guess that's how it works).
As for your suggestion to improve their email/support response time, I believe I've already made a similar suggestion to them in the past, and they say they are working on making that possible.