An investor picked up a 4.9% stake in Interactive Network Inc. Wednesday, but the fledgling interactive TV company’s strategic partners weren’t the sellers, and the company’s chief executive has no idea who the buyer is.CEO David Lockton said he understood the stock was picked up by R.G. Dickenson & Co., the investment firm that underwrote Interactive’s initial public offering in 1991, but likely for a client. “I can guarantee you they didn’t buy it as a principal,” Lockton said. Dickenson officials could not be reached. The investor bought the 450,000 shares for $ 9.13 a piece, or $ 4.1 million. The news sent Interactive’s stock soaring. In Nasdaq trading, the company’s shares climbed $ 1.38 to $ 10.50. Nearly 1.3 million shares changed hands, more than five times Interactive’s average daily volume. Lockton also said the company’s strategic investors — Tele-Communications Inc., NBC and Gannett Co. — were not sellers. Those companies would have had to complete substantial paperwork that would have crossed Lockton’s desk if they wanted to sell their shares. None of that happened, he said. The seller was likely among the handful of brokers and fund managers that have access to a large chunk of Interactive shares to sell, Lockton said. “I don’t really care who’s selling,” Lockton said. “I just want to know who’s buying.” With a sizable piece of Interactive, the investor could theoretically influence corporate decisions. But any buyer would have a difficult time gaining control of the company since Lockton and the strategic partners own 5 million of the company’s 14 million outstanding shares. “Nobody’s going to take control of this company,” Lockton said.