Russia is probably phrasing things so they aren't obligated to get tangled up in something they don't want to be.
Are you coming from the assumption that Russia is too bogged down in Ukraine to engage in another confrontation? Which that doesn't fully take into account or reflect the flexibility of their military capabilities. Russia hasn't been using its most advanced stockpiles in Ukraine and has been relying on older technology.
That could mean they still have considerable reserves of modern weaponry and resources to deploy elsewhere if necessary.
The alliance with Iran shifts the geopolitical landscape in my opinion. Russia's support for Iran could be seen as a way to hedge their bets and solidify influence in the Middle East, especially if there’s the potential for conflict with the West AND their loss of Syria.
In addition, if the U.S. and Israel do indeed take military action against Iran, Russia could respond in ways that escalate the situation, especially with its nuclear and conventional capabilities still intact regardless of Ukraine. The treaty may give them a clearer path to supporting Iran militarily, either through direct intervention or by supplying critical resources and technology.
So, it's not just a matter of Russia being "too busy" in Ukraine, but rather that the geopolitical reality is much more fluid, and
Russia is still a major power with the means to act when it chooses.
For lack of better words, I regularly 'sh*t' on or crudely make fun of the Russian military. But the reality is that Russia is still a credible threat and, in my opinion, still holds a large stockpile of advanced weapons it can use or give to make things much more fluid in an Iran strike, as they have mostly avoided using their advanced weapons in Ukraine. They only use them occasionally, usually just to make a point.
While the war in Ukraine has not gone their way. Again doesn't mean they cannot act when they so choose to still.
Russia can and will likly make any strike on Iran much more complicated.