Upgrades are often confused with Upsells.
What your web friend received was a call from NCL's very small Upsell department. They call you, they do not accept calls.
Upsells are offered to just a few because there's usually only a few empty, expensive cabins (meaning suites) left to sell. Let's assume there's an empty, unsold owner's suite. The Upsell department will offer it to someone who had booked a penthouse suite for 50% the difference. Then they will offer the penthouse suite to someone who had booked a mini suite. The idea is to open up a cheaper cabin that can be sold at the last minute easier. Most will not be offered an upsell because there aren't that many owner's and penthouse suites aboard NCL ships. 50 suites at most, when most NCL ships have 1000 to 1400 cabins.
Upgrades are usually free, and given to those who booked with a cabin guarantee. Guarantee cabins are usually the cheapest cabins in a class. There's just a few (most likely just 4 cabins). For example, there's 4 BE balcony cabins on the Spirit. If they assign you a BD balcony cabin, that's considered an Upgrade.
Whether you get offered an Upsell or not depends upon what cabin is empty, and what you had booked. The likely-hood that NL will offer an owner's suite upsell to someone who had booked an oceanview is extremely small.
While a few other lines might move passengers into empty more expensive suites, NCL prefers to sell them at a significant discount to those who have already booked a cabin.
As I wrote before, the Upsell department is really small, and can't handle many incoming calls. They really don't like incoming calls. and might place you on a "do not call ever list" if you pester them with many incoming calls.
What you can do is pay the full price between what you have already booked and what you want from NCL's regular booking department, or from your travel agent, before Final Payment day.
They really don't offer that many Upsells per cruise.
It's always best to book the class cabin you want from the start.