The strange material discovered on your wall, pink and tough, has led to some intriguing ideas. Although your landlord mentioned it could be sealing foam, the unexpected arrival and feel of it make us consider it might be something more unusual.
One interesting idea is that it may not be a substance, but rather linked to something living, like a reptile or amphibian. Some animals, mainly in warm climates, leave unusual substances that may look like this. For instance, some geckos or frogs can release strange substances, like egg masses, that become hard and crusty. These could be found in strange spots, like on walls, especially if there was a small opening for the creature to get through. Because of its growth-like look, it is possible that the "mystery growth" might have been some kind of deposit, like eggs or waste, that dried up in the heat.
Also, some reptiles, such as lizards, are known to leave their old skins behind, which can appear similar to foam when they dry. Amphibians may lay egg sacs that look like pink jelly at first, but then they dry up and become hard. Although it is uncommon for these events to happen indoors, it is still possible, especially if your building has openings that allow these creatures to enter easily.
In certain damp places, you might find fungi growing, especially in places like Queensland. However, this particular event does not have the usual characteristics of fungus, like a soft feel or visible spores.
Without looking into it more or it happening again, it's difficult to say for sure what the substance was. If it comes back, it may need more attention to check for problems like leaks, mold, or hidden gaps in the wall.