These are the same thing. Russia sells oil to the world, and their currency is based on the price of oil. (It is for this same reason that the Canadian dollar has been sliding.)
Putin has been a competent leader for Russia in many ways, but the failure to diversify the economy from oil is his primary failure. You might say “corruption”, but resource economies are almost always corrupt. The only way to (somewhat) avoid it is to put the money away in a sovereign fund or the equivalent.
It is also important to not allow the currency to become a resource currency, because that crushes all other export businesses.
Why did the price of oil drop? There are a lot of theories, from screw-ups in the futures market, to increased supply and reduced demand, to intent to destroy Russia.
What is interesting is that OPEC (meaning, in this case, Saudi Arabia) has refused to do anything to stabilize oil prices and prevent the collapse.
Saudi Arabia needs higher oil prices, they have no economy other than oil of significance, but they also have more ability to handle oil price collapses. Saudi crude is cheap to produce, under $10/barrel. The profit may be less, but they are making a profit. A lot of Russian, American, Canadian and other oil is not profitable at low prices. Letting oil prices be low for a year or two will probably help Saudia Arabia more in the long run. Certainly it hurts their competitors more than it hurts them.
Many also believe that the US and Saudi Arabia are doing this deliberately to hurt Russia.
Of more fundamental interest is that China has been buying less and less commodities (not just oil, but metals like copper). China is the most important economy in the world now for hard commodity prices.
The Ruble collapse is going to hurt a lot of people, most especially the Europeans. Europe sells a lot of goods and services to Russia, and Russia is no longer going to be able to afford them.
For now, low oil prices will be good for the US, but the general commodity price drops are hammering many other countries, and that will lead to reduced demand globally. This isn’t a good thing, however much many Americans are enjoying Russia (and Putin”s woes.)
I will note also that Russians seem to be blaming the West for the collapse of the Ruble. That’s a good thing if they decide going supine will help them.
It’s not a good thing if they get angry about it and decide the West (meaning the US) is deliberately trying to destroy them.