There is no such thing as a "Best", as each weapon is made to preform a specific role. Just as there is no such thing as a sniper rifle, because a person is a sniper, and any rifle they have in their hand is a "sniper rifle", just like there is no Air Force 1, whatever plane the president of the united states is on is Air Force 1.
"Whatever rifle is in the hands of a sniper" does not equal "a sniper rifle". It equals "a sniper's rifle", and/or "a rifle being used by a sniper for sniping."
"A rifle being used by a sniper for sniping" is not the same thing as "a rifle specifically designed and intended for the purpose of, sniping."
As for being "the best"... I don't know about this rifle in particular, but just because different weapons are made to perform different roles - and each tends to have its own pros and cons, doesn't mean that there cannot be "considered to be the best" when talking about a specific role. Don't ignore the word "considered" there - it doesn't mean that the weapon is, without argument THE best... it simply means that based on a specific set of role-related criteria, it outperforms others in the ways that really matter.
Both my father and (one of) my brother have sniper training (one USAF, the other SWAT). Neither of them would consider my nephew's BB gun to be a sniper rifle, just because of their training and qualification - or even any hopeful or intended use.