Victory, there's a missing detail or two in your request.
I hope you didn't eat much of the roast.
Smelt and tasted gamey = spoiled meat, which usually means mishandling somewhere along it's pre-cook journey.
I suspect that's the cause.
What did the meat smell like when you removed it from the retail packaging?
Did it feel slimy?
Smell and feel are your first line of defence.
What was the purpose of the pre-sear?
Did you suspect something was wrong with the meat?
Did the meat smell bad or off during the sear?
You cooked the meat well past the Pasteurization stage, plenty safe for wholesome meat at the beginning. If you preheated the water while searing and sealing the meat and promptly added it to the water bath it should have been satisfactory.
"A bit tough", indicates its tenderness didn't meet your expectation.
Have you previously cook the same "sirloin" from the same trusted source with a satisfactory outcome? The reason i ask is that where i live a lot of meat cut from the rump is misleadingly labeled "sirloin". Unless it is well-aged meat cut from the rump needs prolonged cooking, at least 24 hours in my experience, significantly longer if you expected beef tenderloin tenderness.