Both of these are infinite, but the set of numbers containing odd numbers is by definition smaller than the set of numbers containing all integers, because it doesn't have the even numbers.
This is provably false - the two sets are the same size. If you take the set of all integers, and then double each number and subtract one, you get the set of odd numbers. Since you haven't removed or added any elements to the initial set, the two sets have the same size.
The size of this set was named Aleph-zero by Cantor.
China is widely suspected of supplying Russia with equipment and materials to support their war, however no-one has adduced anything concrete to support that theory so far.
The article itself doesn't cite much in the way of sources or evidence, other than mentioning a report by Molfar, the open source intelligence agency. Molfar has published reports on the same topic in the past, but there hasn't been anything recently.
If the Telegraph had new information or evidence they would be shouting a lot louder than this. This is most likely them covering up for a quiet day by dredging up some old rumours and repackaging them as news.