This is bullshit propaganda, sorry. Russia has over 1000km of coast at the Black Sea, to the East of Crimea.
I will say, even if it were true, that wouldn't justify what Russia is doing. But I can see how it would be useful for domestic consumption.
Its straight out of Imperial Russia's propaganda book. Kind of proof that Russia since ~1600 has always been the same country, just with a different coat of paint (the one between 1917 and 1991 happening to be red paint).
Putin has almost exclusively bad things to say about the USSR, it is the Russian Empire he wants to restore.
But you contend that Putin doesn't want the western tip of Ukraine, but instead to reclaim Finland, Alaska and parts of Poland? Because that's the only difference in his territorial ambitions.
For one, Putin seems to want to reassemble the USSR as a vanity project. Further, this all started (years ago) when the Ukrainians removed out their Moscow friendly president. Putin doesn't like reminders that months of sustained protests can really effect change and remove leaders, especially so close to Russia.
Crimea is the only "warm water" port that Russia has access to to gain access for the end and the Atlantic.
The Ukraine has a ton of farmland. This may be more valuable soon because China imports a ton of food and if you're planning on a Sino-Russo alliance cut off from western powers, food is important.
Similarly, it shares a lot of the fresh water sources with the rest of Europe. I don't know if it's something he can attempt to monopolize, but controlling water into the region is at least as good as natural gas, and less seasonal with less ability to diversify like to green energy.
The USSR located some specialty heavy industry in Ukraine. If it still exists, it might be valuable. I read, but can not confirm, that it was part of the strategic goal of the USSR to make sure each constituent state wasn't self sufficient to encourage national unity. But that could just be BS. Reasoning like that is almost certainly why Crimea was given to the Ukraine.