It is. Capitalism is a productivist system. To make money, you must produce something (or own something). UBI gives you a revenue on the basis of being a human being; by virtue of nature not through your work, in function of your productivity. It's not opposed to work at all and even encourages it to gain even better living conditions, but it's not necessary for survival. That can be implemented within a mixed economy and already is to a certain degree, but not in a heavily capitalist one due to the role of the State in it.
For reference....
Definition of capitalism | Dictionary.com
Excerpted....
an economic system in which investment in and ownership of the means of production, distribution, and exchange of wealth is made and maintained chiefly by private individuals or corporations, especially as contrasted to cooperatively or state-owned means of wealth.
It's a left-wing form of anarchism based on ownership by usage. It can be classified as a form of socialism since there is a regulatory role of the State and property of the means of production is collectivised, but it's not collectivised to the whole of society or to the State like in a marxist form of socialist, but to those who participate in a that specific venture. Example, in such a system, Amazon wouldn't belong to its investors, nor the State, but to the totality of its employees including its administration staff.
Anarchism would result in capitalism, simply because
people gravitate towards making & trading things.
And under anarchy, there'd be no mechanism to stop it.
Essentially, you'd have entirely unregulated capitalism.
I prefer some regulation, eg, environmental, monopoly
prevention, GAAP, consumer protection.