Actually, it is possible to get to more than 900 hours. This happens exceptionally, but can (and does) happen. Here's how:
Ryanair stick to the 100 hours per month as best they can since this is monitored closely (no argument with that). However, they have a special agreement for 900 hours max in a calendar year (and not a rolling year, which is the industry norm). There are circumstances - such as illness, or joining the airline, or having been on a training course, etc. in which a pilot does not fly and this creates a unique window of opportunity that is best explained by an hypothetical example (which bears an uncanny resemblance to what has happened):
1st three months of year - sick.
1 month of remaining year - leave.
Remaining 8 months of year - fly say 800 hours.
Reach end of year. Flight time zeroed and recommence cycle.
1st four months of new year - fly 400 hours.
Total time in 11-13 months (depending on when leave was taken) = 1200 hours. [This is where your consultant gets his figure].
Even allowing for when the month's leave was taken, you can see how hours in a 12 month period can be much higher than was ever intended.
This cannot be repeated by full-time Ryanair employees that are on a normal roster. However, once an anomaly comes up, or a contractor enters or leaves employment, or a new pilot joins, etc. the potential for "flexibility" comes up. The "zeroing" of time at the end of the calendar year is what makes this work.
Since it cannot be repeated regularly on a planned basis, your "consultant" is, of course, serving his masters well by pointing out something which is literally true, but not really the norm. (I hope you felt bad about your lack of productivity and gave back some money to your employer to compensate for your laziness !).
To be more serious, what this "annual zeroing" means is that exceptional circumstances can be exploited or manipulated. (For example, the above is the reason why some people find their leave is unavailable or why they work much more than colleagues after having been sick for more than a few days). This is alll against the spirit and intention of the original 900 hours in a "rolling year", but you can trust Ryanair to extract every last second of work.
For analogous reasons it is typically through the cancellation of leave that Ryanair can achieve high levels of short-term productivity to overcome pilot shortages (e.g. last summer). The only cost is annoyed pilots, but they have comprehensively demonstrated that they are not too concerned about that! An added advantage of tired pilots is that they complain less.