Is the area burnt in Amazonas quite smaller than the 2018 California wildfires?
It is very likely true. Most of the fires shown on TV and in maps are not in Amazonia and not in true rainforest. Quite a lot of them are not even in Brazil. The amount of Amazonian rainforest burning is therefore relatively small, and is due to land clearance and illegal logging where the trees have been cut down and what is left allowed to dry out in the sun and then burned. Out-of-control wildfires are possible in California, but not in true rainforest, which is too damp.  A few very small fires may be due to forest-dwelling natives clearing a small patch and setting fire to it for slash and burn, short-term cultivation. They will abandon it in about 5 years time when the soil is exhausted and the rainforest will gradually take over again.