The two bits of news that Biondello brings actually both concern the groom-to-be of Katharina, whom Biondello reports as being on his way and about to arrive. Biondello shows how this bit of news is the "new" news with a quip at the expense of Baptista, but then the old news, which is much more interesting, concerns the peculiar appearance of the aforementioned Petruchio, who has chosen to wear a most interesting selection of clothes for his wedding as if to deliberately make both himself and Katharina ridiculous. Note the beginning of the following description:
Why, Petruchio is coming in a new hat and an old jerkin; a pair of old breeches thrice turned; a pair of boots that have beeen candle-cases; one buckled, another laced; an old rusty sword ta'en out of the town armoury, with a broken hilt, and chapless; with two broken points...
Petruchio therefore seems to have deliberately chosen to clothe himself in the most ridiculous garb possible to expose his wife to the ridicule that is part of his method of taming his "shrew," and by having Biondello report it before his arrival our suspense of what Petruchio will actually look like is so much the greater.