Taking a "tonne" as being a metric ton, 150 tonnes is 150 Mg, or 150 million grams. So for this to be a true, a car would have to burn 150g/day.
Gallons used per vehicle (524) dipped 14 percent from 2003, which was its maximum consumption year.
The density of gasoline ranges from 0.71–0.77 kg/L
524 gallons is 1983 liters, giving 1407 kg/year, or 3.857 kg. Thus, if a cruise ship burns 150 tonnes a day, it burns as much as fuel as 38k cars. Only if a cruise ship produces 26 times as much particulates per kg fuel would this make sense.
Also, the claim "more or less the same energy a mid-sized city needs." is quite questionable. If we says that a "mid-sized" cruise ship has 3k passengers, and a "mid-sized" city has 100k population, then this would mean that a cruise ship is providing 33 times as much energy per person as a city. While it makes sense that it would be higher for a cruise ship, 33 times sounds rather high.
There is this, however:
Large ships run on heavy fuel oil, which is legally permitted to contain 3.5% sulphur – that’s 3,500 times what is permitted in road fuel. In EU ports and waters, ships are legally required to switch to a cleaner diesel, but even this, capped at 0.1% sulphur, is allowed to contain up to 100 times more sulphur than road fuel.
So, it appears that are particular types of particulates for which a cruise ship produces as much as one million cars, but the article is poorly worded in implying it is the amount of fuel, and the constant running of engines, rather than the different fuel composition, that causes it. Note also that if cruise ships were not burning this heavy fuel oil, then either it would be burned somewhere else, or not use at all, and the latter would be rather unlikely.