No, language models were not a secondary application transformers. From the abstract of the paper you posted:
> The transformer model has been widely leveraged for natural language processing
and computer vision tasks, but, to the best of our knowledge, has never been used for stock price
prediction task at DSE.
In general, all the fancy DL stuff from the last decade started on either images (e.g. CNNs) or text (e.g. RNNs, transformers). Applying them to tabular data is generally an afterthought, and for time series in particular is rarely worth the time and compute.
The paper you posted is not very good and should not be used to inform your own work. It includes no comparisons to baseline models, and even the abstract describes the results as "acceptable".