Explanation (I apologize for poor English, but I tried my best).
Every epoch has its "magic numbers", the meaning of which is clear to everyone. Such a "magic number" of the post-war Soviet era was "3.62". This is neither the maximum Mach number of the MiG-25, nor the caliber of a secret spy weapon, it is just the price of a half-liter of vodka in rubles, which remained constant for a long time. If we take into account that the cost of a bus or subway fare was 3-5 kopecks (i.e., ca. hundred times cheaper!), it was hard to call Soviet vodka cheap. Thus, a large part of the USSR population consumed alcoholic beverages that were not sold in stores. One of them was moonshine, but one had to pay for it too. Pilots, aviation technicians and partly Soviet Navy sailors had a special privilege - some types of equipment required 60% alcohol solution for cooling. Alcohol used for its production was of food quality, not technical. I don't know for what reasons it was prescribed to use food-grade alcohol, but I guess that they simply tried to prevent mass poisoning with denatured mixtures. The undisputed champions in terms of the amount of alcohol filled into the cooling systems on each flight in the Soviet aviation were two aircraft - Tu-22 and MiG-25. I do not remember the exact figures, but the first should be filled with about 400 liters, the second - with 200 or 250 liters. After each flight, the alcohol solution was supposed to be drained, than the system had to be filled with a fresh portion of coolant for the next flight. It is clear that technicians and pilots utilized the drained alcohol not as prescribed by regulations. Tu-22 though was more profitable, but the risk was too high - the airplane was very complex, the accident rate was one of the highest in Soviet aviation, the number of accidents was depressing. moreover, it was difficult for technicians to maintain it, etc. The MiG-25 was not simple either, and its accident rate was also high at the beginning of its deployment, but still not as high as that of the Tu-22. MiG-25 pilots ejected upward, not downward, as on the Tu-22, which gave them a much better chance to survive the ejection. There were even legends among military pilots that alcoholism was common in Tu-22 regiments (which I highly doubt). The MiG-31 already used for cooling substances unsuitable for "internal use" as alcoholic beverages. Therefore, the attitude towards it was not as cordial as the MiG-25.
The MiG-25 had several nicknames, the most common was probably "food store" ("gastronom" in Russian). I personally never heard "flying restaurant" used, but the meaning is correctly expressed as well.