Tha is the second cell of the dental row, the aspirated voiceless dental. It is not the th of English, which is a fricative made with the tongue between or against the teeth and continuing rather than stopping; it is a t made at the teeth and released with a puff of breath. The confusion is caused entirely by the romanisation, which uses the same two letters for a quite different sound, and it is one of the standard difficulties in reading Sanskrit words in Latin script. In the chart there is no ambiguity, because the cell is defined by its row and its column: dental, voiceless, aspirated. Ranjana draws the letter in the position the order assigns and writes it as it writes every consonant, carrying the inherent short a and hanging from the head bar.
The lesson generalises. A chart of a Brahmic script is unambiguous in a way that its romanisation is not, and reading the position rather than the transliteration is usually the faster route to understanding what a letter is. The confusion is worth dwelling on because it recurs for every aspirate in the chart. In the romanisation of Sanskrit the letter h after a consonant always marks aspiration and never makes a fricative, so th, ph, kh, ch, dh, bh, gh and jh are all single consonants and none of them is the English sound its spelling suggests.