You need to brush up on your Spanish. The author is saying that the total number of Goths did not go beyond the 150,000 figure, it does not necessarily mean that they were not 150,000. Translation of what she says:
"As a conclusion we can say that there does not exist any reliable statistic data, but that, even though all of them are hypothetical, they allow us to think that the number of Visigothic inhabitants of the Iberian Peninsula did not go beyond 130,000 or 150,000 individuals."
She is accepting the 130,000 to 150,000 estimate as plausible, just not more than that. And she is only citing someone else's calculations for the total population of Iberia, she is not necessarily endorsing it. She remains silent about her own conclusions on this topic. She cites several figures from different historians. The author I cited earlier says that the more usual estimate is 6 million inhabitants.